Automatic vehicle transmissions function to transmit torque from an input shaft connected a power source, such as an internal combustion engine or an electric motor, to an output shaft connected to a set of driven wheels. Typically the transmission is provided with a gearing system that includes interlocking gears mounted on rotating shafts designed to vary a ratio of the speed of the input shaft to the speed of the output shaft. In order to increase the efficiency of the gearing system, the system needs to be lubricated.
In addressing this problem it is known to establish a lubrication system by forming lubrication passages in the shafts and gears of the gearing system to allow lubrication oil to be distributed throughout the transmission. The lubrication system also includes a sump at the bottom of the transmission that holds extra lubrication oil. A pump draws lubrication oil from the sump and sends the oil through the lubrication passages to lubricate the various moving parts of the transmission. In the case of a planetary gearshift transmission having multiple interlinked planetary gearsets mounted on several rotating shafts, central lubrication passages are often formed so as to extend axially within each shaft. Radially extending holes are provided at various spots in the rotating shafts to allow the lubrication to travel from the central lubrication passages outwardly through the radial passages to where the oil is needed.
While such designs have proven satisfactory in the past, the performance demands on transmissions have been increasing over time. That is transmissions are required to last longer and carry heavier loads. As a result, transmission designs need to be more resistant to wearing out due to fatigue while carrying heavier torques. In the case of a planetary transmission fatigue, failures can occur at the outer surfaces of the rotating shafts near the radial lubrication passages. Such fatigue failures are particularly problematic on rotating shafts that are subject to heavy loads. To address the problem of heavier loads it is possible to simply increase the shaft diameter of each affected shaft or alternatively use more durable materials. However, increasing a shaft diameter not only requires more material for that shaft, but many other parts of the transmission must be redesigned as many shafts are designed to rotate within each other in a nested, concentric configuration. Furthermore the cost of using more durable materials is significant. In either case the additional cost is unacceptable.
As can be seen by the above discussion, there is a need in the art for a system that will effectively distribute lubricating oil to the various moving parts in a vehicle transmission while allowing the transmission to carry heavy loads. More particularly there is a need for a system that will reduce fatigue failure while not requiring a change in shaft size even though the transmission is designed to transmit more torque over a longer lifespan.